A Pt / O-NCP catalyst and its preparation method

Abstract

This invention discloses a Pt / O-NCP catalyst and its preparation method. It utilizes self-developed nanoporous carbon (NCP) as a support, which is modified to change the internal pores from a hydrophobic to a hydrophilic state. A special preparation method is then used to obtain the noble metal catalyst Pt / O-NCP. During catalyst loading, most Pt nanoparticles are located within the mesopores of the support, maximizing the direct contact between the polymer and Pt (sulfonic acid poisoning). This solves the problems in existing catalysts where Pt nanoparticles are prone to dissolution and carbon corrosion under voltage fluctuations, leading to Pt growth and aggregation, thus avoiding the reduction in catalytic performance caused by a decrease in the active surface area of ​​the catalyst. Furthermore, this catalyst can also address the significant decrease in overpotential of ordinary carbon support materials under low humidity, resolving the typical performance degradation of PEMFCs under low humidity conditions.

Description

Technical Field

[0001] The present invention relates to a catalyst, specifically to a noble metal nanocatalyst Pt / O-NCP supported on modified porous carbon (NCP) and a preparation method thereof; it belongs to the technical field of noble metal nanocatalysts. Background Art

[0002] The growing global energy demand and environmental problems have promoted the development of sustainable energy conversion and storage technologies, and it has become particularly important to develop energy storage and conversion devices compatible with renewable energy. Among them, proton exchange membrane fuel cells (PEMFCs) stand out due to their unique advantages such as zero greenhouse gas emissions, high theoretical power density, and high energy conversion efficiency.

[0003] So far, Pt-based electrocatalysts in the series of noble metal catalysts have always been the only choice for practical PEM fuel cells. Many studies on platinum-free catalysts have been carried out in the prior art. For example, the research and development of non-noble metal transition metals, metal nitrides, and nano-carbon-based metal-free electrocatalysts are in full swing. However, due to the poor stability and limited performance of these catalysts, it is difficult to commercialize these catalysts in the fuel cell industry.

[0004] Therefore, developing Pt-based catalysts for oxygen reduction with high catalytic performance and durability and exploring their large-scale production strategies are the key points for the long-term development of fuel cells. Summary of the Invention

[0005] To solve the deficiencies of the prior art, the purpose of the present invention is to provide a Pt / O-NCP catalyst and a preparation method thereof. The process is easy to implement, the catalyst has better dispersion, and the oxygen reduction performance is greatly improved.

[0006] To achieve the above objectives, the present invention adopts the following technical solutions:

[0007] The present invention first discloses a preparation method of a Pt / O-NCP catalyst, including the following steps:

[0008] S1. Add NCP carbon powder and Co precursor into a mixed solution of ethanol and alcohol, stir evenly by ultrasonic treatment and then stir overnight, and rotary evaporate and dry the mixed solution;

[0009] S2. Heat-treat the dried powder at 200-600 °C under N2 purge for 1-5 h to isolate air and prevent the carbon powder from oxidation, thereby obtaining Co-NCP;

[0010] S3. Add Co-NCP into an acid solution, heat and stir overnight, then filter and wash with distilled water, and dry in an oven to obtain O-NCP;

[0011] S4. Take O-NCP and add it to the ethanol solution. After sonicating and homogenizing, weigh the platinum precursor and add it to the solution. Stir the mixture with sonication and let it sit overnight. Then, dry the solution by rotary evaporation.

[0012] S5. After drying, the carbon powder is first kept at 200-500℃ under H2 purging for 1-6 hours to reduce the precursor; then it is kept at N2 purging for 1-6 hours to purge H2 and harmful gases after the reaction to obtain the catalyst Pt / O-NCP.

[0013] Preferably, the aforementioned Co precursor is a coordination compound of trivalent cobalt, including but not limited to one of [Co(NH3)6]Cl3, [Co(NH3)5H2O]Cl3 or [Co(NH3)5Cl]Cl2.

[0014] More preferably, the aforementioned NCP toner is prepared using the patented method with authorization announcement number CN106457201B, which is the prior research result of the research and development team of this application.

[0015] More preferably, most of the pores of the aforementioned O-NCP are in a hydrophilic state. In this invention, by selecting suitable raw materials and using specific processes and conditions such as rotary evaporation, cobalt precursors such as [Co(NH3)6]Cl3 are dispersed into the mesopores of nanoporous carbon (NCP). Heating causes [Co(NH3)6]Cl3 to decompose into Co(III). The strong oxidizing property of Co(III) oxidizes the mesopores in the porous carbon, modifying the nanoporous carbon (NCP). Specifically, the pores change from a hydrophobic state to a hydrophilic state, allowing the pores to maintain good humidity, which is beneficial to improving the utilization rate of the catalyst.

[0016] More preferably, the mass ratio of the aforementioned Co precursor to NCP toner is (0.05-0.3):1.

[0017] More preferably, the aforementioned acid solution is selected from sulfuric acid, hydrochloric acid, and nitric acid to wash away residual cobalt in the toner.

[0018] More preferably, the aforementioned platinum precursor is selected from one of chloroplatinic acid hexahydrate (H2PtCl6·6H2O), potassium chloroplatinate, and platinum chloride.

[0019] More preferably, the final catalyst platinum loading is about 40% (mass percentage). For example, if the platinum precursor is chloroplatinic acid hexahydrate, the mass ratio of chloroplatinic acid hexahydrate to carbon powder is 1.8:1.

[0020] More preferably, the aforementioned method for preparing a Pt / O-NCP catalyst includes the following steps:

[0021] S1. Add 500 mg NCP carbon powder and 50 mg Co precursor to a mixed solution of ethanol and distilled water, sonicate until homogeneous, and stir overnight; dry the above solution by rotary evaporation at 70°C.

[0022] S2. The dried powder was heat-treated at 400℃ and under N2 purging for 2 hours to obtain Co-NCP;

[0023] S3. Add Co-NCP to H2SO4 with a concentration of 0.5M, heat to 60℃ and stir overnight, then filter and wash with distilled water, and dry in an oven at 50℃ for 10h to obtain O-NCP.

[0024] S4. Take 200 mg of O-NCP and add it to an ethanol solution. Sonicate for 2 hours. After homogenization, weigh 0.358 g of H2PtCl6·6H2O and add it to the solution. Sonicate for 1 hour and stir overnight. Dry the above solution at 70°C by rotary evaporation.

[0025] S5. After drying, the carbon powder is kept at 300℃ in H2 atmosphere for 2 hours and then kept in N2 atmosphere for 2 hours to obtain the target product - the noble metal catalyst Pt / O-NCP.

[0026] In addition, the present invention also claims a Pt / O-NCP catalyst prepared by the method described above.

[0027] The advantages of this invention are:

[0028] (1) This invention uses self-developed nanoporous carbon (NCP) as a support and modifies it to change the pores from a hydrophobic state to a hydrophilic state. Then, a noble metal catalyst Pt / O-NCP is obtained through a special preparation method. During the catalyst loading process, most of the Pt nanoparticles are located in the mesopores of the support, which maximizes the improvement of direct contact between the polymer and Pt (sulfonic acid poisoning). At the same time, the modified mesoporous carbon used in this invention is mostly hydrophilic in its pores, which allows the pores to maintain good humidity and is beneficial to improving the utilization rate of the catalyst.

[0029] (2) The Pt / O-NCP catalyst of this invention solves the problems in the prior art where Pt nanoparticles are prone to dissolution and carbon corrosion during battery operation due to voltage fluctuations, leading to Pt growth and aggregation. This avoids the reduction in catalytic performance caused by a decrease in the active area of ​​the catalyst. Studies have shown that after 5000 cycles of accelerated corrosion on the carbon support of the catalyst of this invention, the catalyst still retains about 80% of its active area, demonstrating good corrosion resistance. Furthermore, this catalyst can also address the significant decrease in overpotential of non-porous carbon support materials under low humidity, resolving the defect in typical PEMFCs of the prior art where performance significantly decreases under low humidity conditions. Attached Figure Description

[0030] Figure 1 The diagram shows the contact angle dynamics of O-NCP and NCP droplets.

[0031] Figure 2 The image shown is a TEM image of the Pt / O-NCP catalyst;

[0032] Figure 3 The figure shows the electrochemical CV curve of the Pt / O-NCP catalyst (CV curve of Pt / O-NCP in N2-saturated 0.5M H2SO4 solution at a scan rate of 10mV / S).

[0033] Figure 4 The figure shows the CV curves of Pt / O-NCP and Pt / C(JM) in O2-saturated 0.5M H2SO4 solution at a scan rate of 10 mV / S and 1600 rpm. Detailed Implementation

[0034] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0035] Unless otherwise specified, all raw materials used in this invention are commercially available. The NCP toner is self-made, with a particle size of approximately 2 μm and a pore size of approximately 10 nm, and was prepared using prior research results authorized under publication number CN106457201B; details are omitted here.

[0036] Example 1

[0037] The method for preparing the noble metal catalyst in this embodiment is as follows:

[0038] S1, 0.5 mg NCP carbon powder, and 0.05 mg Co precursor [Co(NH3)6]Cl3 were added to a mixed solution of ethanol and distilled water, sonicated for 10 min to homogenize, and stirred overnight. The above mixed solution was then dried by rotary evaporation at 70 °C.

[0039] S2. The dried powder was heat-treated at 400℃ and under N2 purging for 2 hours to obtain Co-NCP;

[0040] S3. Add Co-NCP to H2SO4 with a concentration of 0.5M, heat to 60℃ and stir overnight, then filter and wash with distilled water, and dry in an oven at 50℃ for 10h to obtain O-NCP.

[0041] S4. Take 0.2 mg of O-NCP and add it to an ethanol solution. Sonicate for 2 hours until homogeneous. Then weigh 0.358 g of H2PtCl6·6H2O and add it to the solution. Sonicate for 1 hour and stir overnight. Dry the above solution at 70°C by rotary evaporation.

[0042] S5. The dried carbon powder is kept at 300℃ and H2 purging for 2 hours, and then kept at N2 purging for 2 hours to obtain the target product - the noble metal catalyst Pt / O-NCP.

[0043] Example 2

[0044] The method for preparing the noble metal catalyst in this embodiment is as follows:

[0045] S1, 5g NCP carbon powder, and 1g Co precursor [Co(NH3)5Cl]Cl2 were added to a mixed solution of ethanol and distilled water, sonicated for 20 minutes until homogeneous, and then stirred overnight. The above mixed solution was dried by rotary evaporation at 70°C.

[0046] S2. The dried powder was heat-treated at 500℃ and under N2 purging for 5 hours to obtain Co-NCP;

[0047] S3. Co-NCP was added to nitric acid, heated to 70°C and stirred overnight, then washed with distilled water and dried in an oven at 60°C for 12 hours to obtain O-NCP.

[0048] S4. Take 4g of O-NCP and add it to an ethanol solution. Sonicate for 2 hours until homogeneous. Then weigh 7.2g of H2PtCl6·6H2O and add it to the solution. Sonicate for 2 hours and stir overnight. Dry the above solution at 60℃ by rotary evaporation.

[0049] S5. The dried carbon powder is kept at 400℃ and H2 purging for 4 hours, and then kept at 4 hours under N2 purging to obtain the target product - the noble metal catalyst Pt / O-NCP.

[0050] Example 3

[0051] The method for preparing the noble metal catalyst in this embodiment is as follows:

[0052] S1, 3g NCP carbon powder, and 0.8g Co precursor [Co(NH3)5H2O]Cl3 were added to a mixed solution of ethanol and distilled water, sonicated for 15 minutes until homogeneous, and then stirred overnight. The above mixed solution was dried by rotary evaporation at 70°C.

[0053] S2. The dried powder was heat-treated at 600℃ and under N2 purging for 5 hours to obtain Co-NCP;

[0054] S3. Co-NCP was added to nitric acid, heated to 70°C and stirred overnight, then washed with distilled water and dried in an oven at 70°C for 8 hours to obtain O-NCP.

[0055] S4. Take 2g of O-NCP and add it to pure water. Sonicate for 2 hours until homogeneous. Then weigh 3.4g of potassium chloroplatinate and add it to the solution. Sonicate for 1 hour and stir overnight. Dry the above solution at 70℃ by rotary evaporation.

[0056] S5. The dried carbon powder is kept at 500℃ and H2 purging for 6 hours, and then kept at N2 purging for 3 hours to obtain the target product - the noble metal catalyst Pt / O-NCP.

[0057] Example 4

[0058] The method for preparing the noble metal catalyst in this embodiment is as follows:

[0059] S1, 10g NCP carbon powder, and 2.5g Co precursor [Co(NH3)5H2O]Cl3 were added to a mixed solution of ethanol and distilled water, sonicated for 30 minutes until homogeneous, and then stirred overnight. The above mixed solution was dried by rotary evaporation at 70°C.

[0060] S2. The dried powder was heat-treated at 600℃ and under N2 purging for 5 hours to obtain Co-NCP;

[0061] S3. Co-NCP was added to nitric acid, heated to 70°C and stirred overnight, then washed with distilled water and dried in an oven at 70°C for 14 hours to obtain O-NCP.

[0062] S4. Take 8g of O-NCP and add it to acetone solution. Sonicate for 2 hours until homogeneous. Then weigh 9.2g of platinum chloride and add it to the solution. Sonicate for 2 hours and stir overnight. Dry the above solution at 70℃ by rotary evaporation.

[0063] S5. The dried carbon powder is kept at 500℃ and H2 purging for 6 hours, and then kept at 6 hours under N2 purging to obtain the target product - the noble metal catalyst Pt / O-NCP.

[0064] Comparative Example

[0065] This comparative example is a commercially available Pt / C (JM) catalyst, specifically the Johnson Matthey 40% Pt / C catalyst.

[0066] Performance characterization and results analysis

[0067] (1) Hydrophilicity and hydrophobicity test

[0068] Detection method: To measure contact angle dynamics, a carbon powder sample (0.1 g) was pressed into microspheres (25 mm in diameter) using a stainless steel mold at a pressure of 36 MPa for 4 min. Then, a 10 μL water droplet was released to a height of 1 mm on the carbon sphere. The droplet behavior on the carbon particles was captured using a high-speed camera (DRS technology) at a frame rate of 1000 fps and a shutter speed of 0.25 ms.

[0069] Figure 1 The image shown is a continuous image measurement diagram of the contact angle dynamics of water droplets of the O-NCP product in Example 1. The results show the time required for 100% dry carbon particles to completely absorb the water droplets deposited on them. It can be seen that the raw NCP carbon powder is hydrophobic, while the O-NCP carbon powder modified by Co in this invention is hydrophilic. This has a crucial impact on the performance improvement of the subsequent catalyst.

[0070] (2) Transmission electron microscopy (TEM)

[0071] Detection method: 2 mg of carbon was dispersed in 1 mL of ethanol and sonicated for 15 min. This drop of solution was then placed on a copper-carbon coated grid and tested on a JEOL JEM-F200 electron microscope.

[0072] Figure 2 The transmission electron microscopy images show that the Pt particles are uniformly distributed in the pores, with only a small amount of aggregation observed, which maximizes the direct contact between the polymer and Pt (sulfonic acid poisoning).

[0073] (3) Catalyst performance testing

[0074] Detection method: Figure 3 Electrochemical measurements were performed on a CHI660e, using a glassy carbon electrode with a diameter of 7 mm as the working electrode (0.384 cm). 2 Platinum wire was used as the counter electrode, and a reversible hydrogen electrode was used as the reference electrode. All catalysts were dispersed in a mixture containing water, ethanol and Nafion (5%) to form 5 mg / mL ink. 5 μL of ink was dropped onto glassy carbon and dried at room temperature.

[0075] Figure 4 Electrochemical measurements were performed on a CHI660e electrode, with a glassy carbon rotating disk as the working electrode (0.196 cm⁻¹). 2 Platinum wire was used as the counter electrode, and a reversible hydrogen electrode as the reference electrode. All catalysts were dispersed in a mixture containing water, ethanol, and Nafion (5%) to form a 2 mg / mL ink. 5 μL of the ink was dropped onto glassy carbon and dried at room temperature. The final catalyst loading was approximately 20 μg cm⁻¹. -2 .

[0076] Figure 3 The CV curves of the catalyst in N2-saturated 0.5M H2SO4 solution at a scan rate of 10 mV / s and the CV curves after 5000 scans between 1 and 1.5 V are shown. Figure 3 As can be seen, after 5000 cycles of accelerated corrosion, the Pt / O-NCP noble metal catalyst of the present invention can still maintain about 80% of its active surface area, indicating that it has good corrosion resistance.

[0077] Figure 4 The CV curves are shown for a 0.5M H₂SO₄ solution saturated with O₂ at a scan rate of 10 mV / s and 1600 rpm. (Combined with...) Figure 4 Further analysis reveals that the oxygen reduction performance of the catalyst of this invention is significantly improved compared to commercial Pt / C (JM). Specifically, the half-wave potential of Pt / O-NCP is 0.84V, which is 30mV higher than that of commercial Pt / C (JM) at 0.81V. This indicates that the Pt / O-NCP catalyst of this invention has better oxygen reduction performance.

[0078] In summary, this invention utilizes independently developed nanoporous carbon (NCP) as a support and modifies it to change the internal pores from a hydrophobic state to a hydrophilic state. During subsequent catalyst loading, most Pt nanoparticles are located within the mesopores of the support, maximizing the improvement of direct contact between the polymer and Pt (sulfonic acid poisoning). Simultaneously, the modified mesoporous carbon used in this invention maintains a hydrophilic state within the pores, allowing for better humidity retention, which is beneficial for preserving the active surface area of ​​the catalyst and thus improving catalyst utilization. This addresses the typical performance degradation of PEMFCs in existing technologies under low humidity conditions.

[0079] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the above embodiments do not limit the present invention in any way, and all technical solutions obtained by equivalent substitution or equivalent transformation fall within the protection scope of the present invention.

Claims

1. A method for preparing a Pt / O-NCP catalyst, characterized by, Includes the following steps: S1. Add NCP carbon powder and Co precursor together to a mixed solution of ethanol and alcohol, sonicate to homogenize, stir overnight, and then dry the mixed solution by rotary evaporation. The Co precursor is a coordination compound of trivalent cobalt, selected from one of [Co(NH3)6]Cl3, [Co(NH3)5H2O]Cl3 or [Co(NH3)5Cl]Cl2. S2. The dried powder is heat-treated at 200~600℃ and under N2 purging for 1~5h to obtain Co-NCP; S3. Add Co-NCP to the acid solution, heat and stir overnight, then filter and wash with distilled water, and dry in an oven to obtain O-NCP; S4. Take O-NCP and add it to the ethanol solution. After sonicating and homogenizing, weigh the platinum precursor and add it to the solution. Stir the mixture with sonication and let it sit overnight. Then, dry the solution by rotary evaporation. S5. The dried carbon powder is first kept at 200~500℃ under H2 purging for 1~6h, and then under N2 purging for 1~6h to obtain the catalyst Pt / O-NCP.

2. The method for preparing a Pt / O-NCP catalyst according to claim 1, characterized by, The pores of the O-NCP are in a hydrophilic state.

3. The method for preparing a Pt / O-NCP catalyst according to claim 1, characterized in that, The mass ratio of the Co precursor to NCP toner is (0.05~0.3):

1.

4. The method for preparing a Pt / O-NCP catalyst according to claim 1, characterized in that, In step S3, the acid solution is selected from sulfuric acid, hydrochloric acid, and nitric acid.

5. The method for preparing a Pt / O-NCP catalyst according to claim 1, characterized in that, The platinum precursor is selected from one of chloroplatinic acid hexahydrate, potassium chloroplatinate, and platinum chloride.

6. The method for preparing a Pt / O-NCP catalyst according to claim 1, characterized in that, The platinum precursor has a loading mass percentage of 40%.

7. A method for preparing a Pt / O-NCP catalyst according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1. Add 500 mg NCP carbon powder and 50 mg Co precursor to a mixed solution of ethanol and distilled water, sonicate until homogeneous, and stir overnight; dry the above solution by rotary evaporation at 70°C. S2. The dried powder was heat-treated at 400℃ and under N2 purging for 2 hours to obtain Co-NCP; S3. Add Co-NCP to H2SO4 with a concentration of 0.5M, heat to 60℃ and stir overnight, then filter and wash with distilled water, and dry in an oven at 50℃ for 10h to obtain O-NCP. S4. Take 200 mg of O-NCP and add it to an ethanol solution. Sonicate for 2 hours. After homogenization, weigh 0.358 g of H2PtCl6·6H2O and add it to the solution. Sonicate for 1 hour and stir overnight. Dry the above solution at 70°C by rotary evaporation. S5. After drying, the carbon powder is kept at 300℃ in H2 atmosphere for 2 hours and then kept in N2 atmosphere for 2 hours to obtain the target product - the noble metal catalyst Pt / O-NCP.

8. A Pt / O-NCP catalyst, characterized in that, It is prepared by the method described in any one of claims 1 to 7.

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